Generally, an LCD substrate is formed of two glass substrates. One substrate is a substrate on which a color filter is formed, and the other substrate is a substrate on which a thin film transistor (TFT) array is formed. The LCD color filter includes three primary colors, i.e., red, green and blue, and represents a color using a combination thereof.
A flatness of the glass substrate is a very important factor in the LCD color filter. Accordingly, a grinding process is performed after a process of forming an LCD color filter. In order to grind the LCD color filter, a process of measuring a three-dimensional image of the LCD color filter is performed. Generally, the measuring process is performed using a confocal microscope in a non-contact manner.
The confocal microscope has a small diameter pinhole between a light source and a light receiving device. In addition, light emitted from a point light source is concentrated to a point corresponding to a focus of an object surface by an object lens of a microscope, and the light reflected from the concentrated part is partially reflected by the object lens, passes through the pinhole, and then imaged on the light receiving device. At this time, when a position of the measurement surface is deviated from the focus, most light is blocked by the pinhole formed at a front end of the light receiving device, and only when the position of the measurement surface corresponds to the focus, most light can pass through the pin hole.
Since the confocal microscope employs a point-to-point imaging method, it is possible to obtain a clearer image than a general microscope and three-dimensional image information by appropriately scanning a position of the focus along the surface of the measurement object in a depth direction.
However, the confocal microscope is usually too expensive to use for measuring a three-dimensional image.